Some of the nation's banks are revisiting a disturbing episode in their very recent history. They're mailing out letters to four million people. It's part of a massive review of home foreclosures in 2009 and 2010 in the immediate aftermath of the financial crisis. After reaching a compromise on this issue with the Federal Reserve and two other agencies, banks and mortgage servicing companies are having to ask if some people facing foreclosure were treated unfairly. NPR's Chris Arnold reports.

CHRIS ARNOLD, BYLINE: Federal officials have ordered the banks to find people who have suffered financial harm due to the banks' mistakes and to offer those people remediation. And many housing experts say that a lot of people have been harmed. They say in the worst cases the banks are foreclosing when they shouldn't be.

THOMAS COX: To me the chaos is just astonishing.

ARNOLD: Thomas Cox is a lawyer in Maine who's been helping homeowners. And he actually understands foreclosures very well, because 20 years ago he was the one foreclosing on people.

COX: I did a lot of work in the foreclosure arena for the banks and for the FDIC.

ARNOLD: But Cox says back then everything was done by the book. So a few years ago, when he got into doing volunteer legal help for homeowners, he says he was shocked by how sloppy and mistake-ridden everything was.

COX: What struck me at that time was how obscure and deceptive the foreclosure process had become. It appeared that they were not being careful and they were not being accurate in their work.

ARNOLD: Some experts who've scrutinized the banks over the past few years believe that tens of thousands of homeowners have been foreclosed on and put out of their houses when they shouldn't have been, many because they didn't get what's called a loan modification.

SHEILA FRANK: I worry about this all the time.

ARNOLD: In a rural area near Portland, Maine, Sheila Frank is showing us around her house that she built with her husband back 38 years ago.

FRANK: We just all worked together on it, relatives and friends. And you know, we were in our early 20s so it was all pretty cool.

ARNOLD: After the recession set in, Sheila Frank lost her job at the retailer LL Bean. She had a small pension, but not much more. And she and her husband had been divorced many years before. And she suddenly couldn't afford her mortgage. But if she had a lower interest rate she could afford it. And that made her a perfect candidate for President Obama's loan modification program. So she called her lender, CitiMortgage.

FRANK: I talked to them and I just gave them my scenario and she was, yup, that's just the people we're looking to help, and you fit. And she said, you know, my interest rate potentially would be two percent.

ARNOLD: Frank said she did everything the bank asked her to do, but she didn't get a loan modification. Over the next year, Frank says the bank repeatedly lost documents that she sent. She says the bank also told her that she didn't have to make payments for a few months, until she got a new payment schedule. But it turns out that that wasn't true. And missing those payments put her into default.

In April of 2010, she called the bank and was pretty horrified to learn that a foreclosure sale date had been set and it was just two weeks away.

FRANK: How does that work? They've been telling me everything's cool, I've made my payments, and in two weeks they're selling the house I've lived in for 38 years? And I thought I'm going to die.

ARNOLD: Sheila Frank was able to get a state court to block the foreclosure sale with the help of the attorney Tom Cox. They have a court hearing later this month.

CitiMortgage, for its part, declined to go into details but said its actions were appropriate. But in a statement it also said that it will work with Sheila Frank and her lawyer. Tom Cox, though, says most homeowners are not lucky enough to get free legal advice.

CHRISTINA KING: Not only have we lost our house, but it's been completely destroyed.

ARNOLD: That's Christina King from Neenah, Wisconsin. She's another homeowner who NPR is following. In her case, Bank of America in a letter admitted that it had made a mistake rejecting her for a loan modification and then it finally offered her one. But that was a year after she was already out of her house. Since then, the bank failed to winterize her empty house.

KING: There is water in the basement filled with sewage that is filled all the way up to the first floor floorboards. Then there's also burst pipes. And then we see mold - black mold, discoloration, all the way up the walls in the first floor.

ARNOLD: Meanwhile, the Kings have eight young children. They rented a house, and then it got sold. And now they've ended up living in a church rectory.

KING: We have a place to stay, but the kids really miss their house. They miss their friends. They miss their neighborhood.

ARNOLD: After NPR contacted Bank of America, the bank pledged to repair the King's house. But this case was not part of the new review that's just getting underway around the country. And housing advocates are skeptical that very many homeowners are going to get much help through that review. But the federal banking regulators who mandated it say they're optimistic.